The continuing development of portable electrically powered devices such as tape recorders and playback machines, radio transmitters and receivers, and the like, creates a continuing demand for the development of reliable, long service life cells or batteries for their operations. Recently developed electrochemical cell systems that will provide a long service life utilize highly reactive anode materials such as lithium, sodium and the like, in conjunction with high energy density nonaqueous liquid cathode materials and a suitable salt.
It has recently been disclosed in the literature that certain materials are capable of acting both as an electrolyte carrier, i.e., as a solvent for the electrolyte salt, and as the active cathode for a nonaqueous electrochemical cell. British Pat. No. 1,409,307 discloses a nonaqueous electrochemical cell comprising an anode, a cathode collector and a cathode-electrolyte, said cathode-electrolyte comprising a solution of an ionically conductive solute dissolved in an active cathode depolarizer wherein said active cathode depolarizer comprises a liquid oxyhalide of an element of Group V or Group VI of the Periodic Table. The "Periodic Table" is the Periodic Table of Elements as set forth on the inside back cover of the Handbook of Chemistry and Physics, 48th Edition, The Chemical Rubber Co., Cleveland, Ohio, 1967-1968. For example, such nonaqueous cathode materials would include sulfuryl chloride, thionyl chloride, phosphorus oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide and selenium oxychloride.
Another class of liquid cathode materials would be the halides of an element of Group IV to Group VI of the Periodic Table. For example, such nonaqueous cathode materials would include sulfur monochloride, sulfur monobromide, selenium tetrafluoride, selenium monobromide, thiophosphoryl chloride, thiophosphoryl bromide, vanadium pentafluoride, lead tetrachloride, titanium tetrachloride, disulfur decafluoride, tin bromide trichloride, tin dibromide dichloride and tin tribromide chloride.
The cathode collector for use in cells employing the above cathode materials has to be electronically conductive so as to function as a current collector plus electronic conductor to the positive (cathode) terminal of a cell. In other words, the cathode collector is a situs for the electrochemical reduction reaction of the active cathode material and the electronic conductor to the cathode terminal of the cell. The preferred cathode collector material is a carbonaceous material with PG,4 acetylene black and graphite being preferable. In addition to the above characteristics, the cathode collector in some applications must be capable of being molded into various size discrete bodies that can be handled without cracking or breaking. To impart a cohesive characteristic to carbonaceous cathode collectors, a suitable binder material should be added to the particulate cathode collector materials in an amount that will not mask the surface of the carbon particles and/or reduce the available surface of the carbon, thereby unacceptably reducing the activation site areas required for the cathode electrochemical process of the cell. The difficulty in selecting the proper amount of binder to be used is that while the addition of the binder will impart a cohesive characteristic to the carbonaceous cathode collector, it also masks the surface of the carbon particles and/or reduces the available surface of the carbon. Thus for increased serviceability of the cell, less binder should be used while for better handleability and strength of the cathode collector, more binder should be employed.
It is therefore an object of this invention to provide a cathode collector for nonaqueous cells that has good handleability and strength characteristics while also possessing good surface availability which can be used as activation site areas for the cathode electrochemical process of cells employing liquid cathodes.
Another object of the present invention is to provide a plastic-bonded cathode collector with a surface coating of a vinyl polymer that provides good strength characteristics so that the collector can be handled without cracking or breaking during its assembly into a cell.
Another object of the present invention is to provide a vinyl-coated, plastic-bonded cathode collector ideally suited as a component of an oxyhalide/lithium cell since, once the collector is assembled in a cell, the vinyl coating will eventually dissolve in the oxyhalide and thereby help to alleviate the voltage delay that normally is observed with these types of cells.
The foregoing objects will become more fully apparent from the description hereinafter provided.